The invention relates to the preparation of an essentially anhydrous magnesium chloride support for use in the polymerization of 1-olefins. More particularly, it relates to a process for forming magnesium chloride in an improved reaction medium. The magnesium chloride, upon workup and treatment with titanium halide, provides a superior transition metal component for use in the polymerization of 1-olefins.
As is well known in the art, effective catalysts for polymerization of 1-olefins are Ziegler-Natta catalysts obtained by combining transition metal compounds of Groups IVb to VIb of the periodic table with organometallic compounds of Groups I to III of the table. It also is known that these catalysts can be made more effective by depositing the transition metal compound on an inorganic support.
Representative of the inorganic supports shown in the art are magnesium and titanium oxides, aluminum silicate, magnesium carbonate, magnesium chloride, magnesium hydroxide, magnesium alkoxides and complex oxides of magnesium and aluminum. These supports usually require activation either prior to or following deposition of the transition metal compound on the support, activation generally being accomplished by ball milling or by calcination. As a consequence, it has been difficult to control the particle size of the solid support and to obtain sufficient catalytic activity and mileage from the transition metal compound that the catalyst need not be removed from the polyolefin product.
It has been shown in U.S. Pat. No. 4,277,372 that a magnesium chloride support can be advantageously formed by first contacting a hydrocarbon solution of a magnesium alkanoate with a hydrocarbon solution of an alkylaluminum dichloride, then isolating the resulting magnesium chloride particles, subjecting them to several hydrocarbon washes, treating them with an electron donor and again washing them with a hydrocarbon.
Now it has been found that the method disclosed in U.S. Pat. No. 4,277,372 is improved when the hydrocarbon solution of magnesium alkanoate and the hydrocarbon solution of alkylaluminum dichloride are contacted in a liquid hydrocarbon reaction medium containing alkylaluminum dichloride and alkylaluminum alkanoate chloride. The magnesium chloride, thus formed is isolated from the liquid hydrocarbon reaction medium, then worked up and treated with a titanium halide. The resulting transition metal component is used in the Ziegler-Natta catalyzed polymerization of 1-olefins with the effect of forming polyolefins having a narrow particle size distribution and a high bulk density.